Threaded caps have been in common use as closures for the capping of jars, bottles, and similar containers for many years. Typical cap construction is often as a single metal or molded plastic closure or as a combination of two or more components to achieve specific functional or performance characteristics. In typical embodiments the caps are fitted with an additional sealing gasket material, or “liner” in industry parlance, and then threaded tightly onto a container to prevent leakage as well as to aid in the preservation of the contents. This lining or gasket material then becomes the second component in a one-piece cap or the third component in a two-part cap.
For both aesthetic and functional reasons, two-part caps are often constructed with an inner cap and outer shell cover with these two components of the same or of different materials. The inner-cap typically contains internal threads to allow a screw closure onto a container and is fabricated from a material with desirable physical and chemical resistant properties for the specific end-use or product application. The outer cover is often formed of a more rugged material for physical protection of the container and contents and/or a material which may be more aesthetically appealing.
While two-part caps are routinely used as closures, the two piece construction technique is sometimes problematical due to spurious physical relative rotation of the respective parts or the separation of the inner-cap from the outer cover. Either of these common modes of failure results in undesirable and often unacceptable product performance.
One conventional prior art cap is constructed from a molded plastic cap that is then covered with a formed metal over-shell. In another prior art embodiment, a plastic inner-cap is inserted into an outer cover that is molded from a different plastic resin. In these and similar prior art embodiments, the inner and outer components are typically held in relative position by simple frictional engagement. In an alternative arrangement, the frictional engagement between the inner and outer components is further enhanced with minimal mechanical interference tabs or points. Adhesive may also be used in some constructions to augment the frictional and/or mechanical interference engagement. Thus, typical two-piece construction caps rely upon limited frictional and/or minimal mechanical interference possibly augmented with adhesive, to resist unwanted separation or relative rotation.
In all of these arrangements the connection between the outer and inner components must resist the substantial rotational torque occurring during removal and replacement of the cap assembly on a container, as well as tensile loads occurring during normal handling of the package. Since many applications may involve the repeated opening and closing of the containers, the components and their performance must remain constant over time to allow the closure to function effectively through extended use and in a wide range of service conditions.
It is therefore an object of the invention to provide an improved two part cap wherein an inner-element and outer-shell are held firmly together as to provide a structure with reliable and consistent performance.